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Reddragon

Cut and shut steering stem, safe or not ?

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I'm looking to put a radial R 1 front end in my bandit project, from what I can see the bandit stem is a bit longer , so I'm wondering about cutting the yam stem and making a slug to space the 2 halves apart then welding it back together, or should I just get a bandit stem and swap it into the yam yokes ? 

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7 minutes ago, Reddragon said:

I'm looking to put a radial R 1 front end in my bandit project, from what I can see the bandit stem is a bit longer , so I'm wondering about cutting the yam stem and making a slug to space the 2 halves apart then welding it back together, or should I just get a bandit stem and swap it into the yam yokes ? 

Just fit the bandit stem to the r1 yokes, if they are the same size press out press in easy, if not make up a sleeve to fit or use slingshot 750 yokes as they are I believe , 50/54mm as well:tu

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Was just trying to do it in house, I don't have a press but I do have a lathe and a welder , and yes they should fit the slingshot yokes but I wanted the whole deal (y)

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The stem on the R1 forks is Alloy I believe, and probably a type that won't take to welding particularly well.   If you have a lathe make up a new stem.

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Ahh hadn't even considered that it wasn't steel, cant weld ally anyway.  As for making a new stem its only a small basic lathe and i cant cut threads on it 

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what to actually do - as suggested - however the question itself ( generic aspect of joining two stem parts together )is an interesting one that I have also pondered but not done

please - someone correct if i'm speaking bollocks - the way I see it with regards to structural strength = its no brainer - the lower bearing is doing the majority of work / load - the upper bearing is subjected to much less - as both bearings are typically tapered rollers, the bit of stem in the middle is not seeing much abuse ( the bending is going through the triple clamps and forks )

where the issue - in my mind with respect to welding two ends together is simply the accuracy of getting it straight - not "looks good straight" but bang on to a thou or less such that both bearings are running true to each other - not an easy thing to achieve with a welder - probably need to make up a nice snug fit tube to sleeve over and support both pieces - weld up via an access hole in the tube to the root - nice solid tacks - even then - remove the tube to finish off and there's still possibility for pulling

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Its just something i read years ago on a forum when a stem was too short, cut it ,machine up a slug to fit inside with a step in the  middle to space the 2 halves and keep them true then weld it  all up 

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As the R1 stem is alloy, I'd go with a B12 stem. Even a B6 one might do you? Take it along to your local engineering company, and they should press the two stems out, and re-fit the Bandit one for beer money!

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I've cut n shut  steel stems before.  Not a big deal if done properly.  I decided it wasn't much more hassle to machine up a stem for the last conversion I did though.

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thanks for "been there done it" responses - I can see how making a stepped slug and a wee trim off the ID in the lathe to match the slug - nice and tight = will keep it straight :tu one in the bank for future 

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1 hour ago, Gsxrsam said:

Why not use a slingy stem?  tis shorter.....

Thats the original problem,  the  r 1 stem is too short for the bandit headstock 

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1 hour ago, Reddragon said:

Thats the original problem,  the  r 1 stem is too short for the bandit headstock 

Ah ok, read it as bandit too long, missed the bandit frame bit.......

 

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have cut the stem before, tapped inside of both halves and fitted a new section with threads on either side, if your wanting to do in house, do it that way, use one long thread to join them with a spacer, also tapped to suit thread ?

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Interesting idea, but I'll send it to Garry to press out and swap over, last time I tried pressing a stem out in my vice I snapped the vice clean in half 9_9

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Yeah I didn't need the stem so I cut it short so it'd fit in the vice, put a huge socket behind it and did it up tight, then put a scaffold pole on the handle and pulled some more 9_9 Bang! I thought cool it's gone, oh shit no it hasn't :D . It was a decent vice too, a big old record one I'd had for 20 years 9_9

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...... can you imagine that shaft snapping where the joint is when it comes time to replace the bearing .... fuckn hack.... just put a proper shaft in there..... 

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Personally I don't have problem with cutting & shutting a steel stem as has been suggested. I have done it many times & the fact that modern bikes use alloy stems shows that the loads in use are not as big as you might think. I wouldn't cut & weld an alloy stem though for metallurgical reasons as has already been said. For the same reasons I would always use 7075 alloy to make a stem from scratch. 

I would prefer to use steel though just for the extra safety factor

Edited by coombehouse

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On 11/15/2017 at 1:51 AM, nlovien said:

where the issue - in my mind with respect to welding two ends together is simply the accuracy of getting it straight - not "looks good straight" but bang on to a thou or less such that both bearings are running true to each other

It's not a shaft doing 10,000rpm - they don't have to be *that* true to each other. Heck, they never do a full rotation.

I'd have no issues with a welded alloy stem - the section in the centre is really only seeing a tension load, and you'll pull the threads off the preload nut well before you hurt a 1" diameter bit of tigged alloy tube.

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